Modify/override how numbers get stringified in Lua

[cableray]

I am trying to change from a C runtime to a JS runtime, and am running into issues with the int32 type. Lua code which I can't modify is concatenating "33 bit" numbers (>= 2^31) to strings. Lua correctly internally represents these as floats, but somewhat annoyingly stringifies them with a trailing .0 when concatenating. This is annoying because it causes differences in output compared to the C Lua that I was previously using as the runtime. So I was trying to solve this, and was curious if there might be some way to change how numbers get stringified. Can I somehow modify this behavior, so that for large floats lua drops the trailing .0 if there is no fractional part? I'd like to do this without having to modify my existing code (except for maybe modifying _G or simmilar before my code runs) in any way. That means solutions like wrapping numeric values with string.format('%.0f', foo) unfourtunately don't work for my use case.

Javascript BigInts (#128) might work when implemented, but I'm looking for an immediate solution if available.

For more context, see here on stack overflow

[daurnimator]

fengari's behaviour intentionally matches Lua 5.3 here. See LUA_COMPAT_FLOATSTRING and https://www.lua.org/source/5.3/lobject.c.html#luaO_tostring
and the matching fengari code:

fengari/src/lobject.js

Lines 592 to 594 in 0c9631c

	if (!LUA_COMPAT_FLOATSTRING && /^[-0123456789]+$/.test(str)) { /* looks like an int? */
	str += '.0'; /* adds '.0' to result: lua_getlocaledecpoint removed as optimisation */
	}

This is documented here:

fengari/src/luaconf.js

Lines 123 to 129 in 0c9631c

	/*
	@@ LUA_COMPAT_FLOATSTRING makes Lua format integral floats without a
	@@ a float mark ('.0').
	** This macro is not on by default even in compatibility mode,
	** because this is not really an incompatibility.
	*/
	const LUA_COMPAT_FLOATSTRING = conf.LUA_COMPAT_FLOATSTRING || false;

[cableray]

That solves my issue nicely.